The photocatalytic reforming of oxy-hydrocarbons has been studied in some detail over Pd-titania systems. The reaction was carried out under anaerobic conditions and offers an environmentally-friendly alternative method for hydrogen gas generation. Analysis of a variety of TiO2 powders showed that only anatase phase TiO2 were active in the photoreforming reaction. The activity also showed an inverse relationship with the surface hydroxyl group of TiO2. By exploring the effect of molecular structure on the rate of hydrogen evolution from a variety of alcohols over Pd/TiO2 catalysts, a few simple rules are derived that predict the relative rates of photocatalytic reforming and the dominant reaction products. The rate of hydrogen evolution for a range of molecules shows a linear relationship with the stoichiometrically available molecular hydrogen content. For an alcohol CxHyOH, decarbonylation dominates with the formation of CO2 and a hydrocarbon Cxi- The mechanism involves decomposition of oxygenates on the metal surface producing hydrogen gas and the formation of adsorbed CO. The latter is subsequently oxidized by an oxygen species (O") generated in the semiconductor by UV light. Desorption of the resulting CO2 enables another alcohol molecule to adsorb, restarting the cycle. Water is reduced at the TiO2 hole replacing the lost anion and generating further hydrogen. Silicon has been proposed as a potential sensitizer for photocatalysts because its small band gap would allow excitations from wavelengths that are out of reach of semiconductors such as TiO2. Therefore, the stability of the silicon surface towards air and water in the presence of UV light is an important parameter and it was explored in this study. Silicon nanoparticles suspended in water undergo photo-oxidation when exposed to UV light generating hydrogen gas. Ajinealing the silicon nanoparticles to 100 C before exposure to UV light reduces the rate of hydrogen formation. The effect of the heating is to anneal the surface defects in the very outer layer creating a passivating stoichiometric SiO2 layer without significantly increasing the oxide thickness.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:585232 |
| Date | January 2011 |
| Creators | Bahruji, Hasliza |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://orca.cf.ac.uk/55114/ |
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